The present invention relates to the field of internal combustion engines, more particularly to a method of controlling the engine intake and exhaust valves so as to produce a more efficient combustion process within the cylinder and to operate the engine as a pneumatic hybrid.
This invention describes a method for increasing the flexibility of the present valve control. While the general principles and teachings disclosed are applicable to all valve controlled internal combustion engines, the invention is hereinafter described in detail in connection with its application to a reciprocating, cam and valve, multi-cylinder engine.
The poppet valve driven by a camshaft has been used in the internal combustion engine for many years. Modifications to the valve train have been developed to permit changing the valve timing while the engine is in operation. When the timing control prevents the valves from opening during an engine cycle, the cylinder is disabled, and the effect of a variable displacement engine is obtained. The advantage of a variable displacement engine is that when less than maximum efficiency power is required, some of the cylinders may be disabled and the remaining active cylinders' power is increased so that they will operate at greater efficiency, while the engine output remains constant. This approach has had limited success in practice because the usual control activates or deactivates half the number of cylinders, and this abrupt change in output torque causes poor drivability. Furthermore, the disabling mechanism is relatively slow acting so that more than one revolution of the crankshaft is required to make the change.
All of the differences cited with the prior art referenced in my previous application (Ser. No. 09/519,635) apply to the present invention. In addition, there have been camless engine valves developed which eliminate the camshaft, and power the valves with solenoid devices under the control of a computer. These valves tend to be heavy, noisy, and consume large amounts of electrical power, primarily because they utilize magnetic force to move the valves.
One example of these camless valve trains is shown in U.S. Pat. No. 5,199,392 issued to Kreuter et al on Apr. 6, 1993. In order to lessen the solenoid force required to move the valve, three springs are used with the lower two having a combined force equal and opposite to the upper spring with the valve midway between the open and closed positions. The third spring has been added to bias the total spring forces toward the valve closed position and assure a constant neutral point over the service life of the assembly. In addition to the solenoids having to deliver the energy required for the initial spring compression, they must also supply the frictional energy required by each valve operation. The differential spring pressure accelerates the moving mass to the mid (equilibrium) point of the travel and then the opposite differential spring pressure decelerates the moving mass. The system frictional energy reduces the amplitude of spring oscillation each time, so the frictional energy must be supplied by the solenoid towards which the mass is moving. Since the solenoid attractive force increases as the air gap decreases, this results in an impact of the moving mass on the stationary magnet face and or the valve seat. The solenoid electrical energy comes from the fuel powering the engine while driving an electrical generator with its additional losses.
The present invention supplies the energy to move the valves by the more efficient method of a cam compressing a spring. Much lower power electromagnets are used which merely hold and release the valve elements without moving them. The cam compresses the spring to store the additional frictional energy required for both the opening and closing oscillations.
An effort to soften the impact on the magnets and valve seats is shown in U.S. Pat. No. 5,730,091 issued to Diehl et al on Mar. 24, 1998. This invention uses two plates with three electromagnets and 3 springs and provides for a partially open valve position and reduced impacts. These additional components increase the mass and friction of the moving elements of the system, requiring more power from the electromagnets. Partial opening of the valve increases the flow losses across the valve opening and is less desirable than the full opening for one half the open time. The impact reduction is achieved by the third spring resisting the valve spring but with no damping means to handle the transient oscillation between the two springs.
The present invention uses the conventional cam and rocker arm to move the valve. It uses a disabling spring to store the cam energy for release by the electromagnets and stores enough cam energy to provide for the friction losses. A pneumatic damper is employed to absorb the disabling spring reset energy.
U.S. Pat. No. 5,868,108 issued Feb. 9, 1999, to Schmitz et al is another attempt to give a solenoid operated engine valve a "soft" landing. This approach controls the magnetic field strength as the armature approaches the stator by changing the coil ampere-turns to match the reset spring force. It is very difficult to accomplish this control in light of the non-linear relationship of the magnet attractive force versus the spring force and the natural oscillation resulting from their interaction. With the addition of the spring (9), this non-linearity will be difficult to control, especially when the engine speed requires rapid valve action.
In the present invention, the oscillatory action between the two springs will be uniform and repeatable without the need for magnet control. The magnetic attraction is used only for sealing the seating of the armature when the springs have closed the magnetic circuit at the end of an oscillatory excursion.
U.S. Pat. No. 4,917,056 issued Apr. 17, 1990 to Yagi et al describes a valve control having a separate spring which is compressed by the cam directly in a manner similar to the present invention. The fourteenth embodiment (FIG. 36) of that invention has the greatest similarity to the present invention. This embodiment has the valve spring (11), disabler spring (113), hydraulic damper (117), and holding electromagnet (A1) of all the other embodiments and in addition has a second holding electromagnet (A2). This patent does not employ an oscillatory exchange of energy between the springs as does the present invention, but rather a direct force from the cam through the disabler spring and the damper to the valve spring. When the electromagnet A1 releases the valve, any oscillatory energy exchange is suppressed by the damper. Therefore, the A1 release merely opens the valve (as quickly as allowed by the damper) to the opening called for by the cam profile, unlike the immediate full opening of the present invention. In a similar manner, the early closing of the valve described merely releases the valve (only after it has reached the full open position and is latched) from the full open position to that allowed by the cam profile at that time and the valve does not fully close until the usual time. In the present invention, the valve opens rapidly (no damper), independent of engine speed, to the full open position and fully closes rapidly (no damper), again independent of engine speed.
The fluid in the hydraulic damper must be adjusted to accommodate changing engine speeds since the inertia forces depend upon cam speed. In the present invention, the pneumatic damper for spring reset needs no such adjustment since it is fixed by the release of a spring compressed to the same point independent of speed.
It is not possible with these embodiments to operate the valve outside of the range of the cam lobe. With a pneumatic hybrid, it is desirable to operate the engine as an air motor and thus utilize braking energy to propel the vehicle. If the catalyst is to be protected from the exhaust of the air motor, it is necessary to interchange the valve functions so that the intake valve may be opened on the exhaust stroke and the exhaust valve opened on the intake stroke. The present invention has this capability because the cam energy is stored in the disable spring before valve operation is required.